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Abstract:

A process for three-dimensional modeling in which water soluble
thermoplastic material is used in an additive deposition process to form
a soluble support structure for a three-dimensional model formed via
layer-by-layer deposition of the model's geometry. The water-soluble
thermoplastic material includes a base of vinyl alcohol. Following the
completion of the model, the model is placed in a cold water bath to
dissolve the support structure. The water-soluble material can also be
used to form soluble model directly.

Claims:

1. In a process for making a three-dimensional object by dispensing
solidifiable modeling material in a predetermined pattern so as to define
the three-dimensional object in coordination with dispensing solidifiable
support material so as to define a support structure for the
three-dimensional object, the support structure thereby having portions
thereof in contact with the object, the improvement comprising: forming
at least those portions of the support structure contacting the object
from an amorphous vinyl alcohol polymer.

2. A process for making a three-dimensional object as defined in claim 1
wherein the amorphous vinyl alcohol polymer is a G-Polymer®.

3. A process as defined in claim 2 wherein the G-Polymer is mixed with
additives to reduce the stiffness of the G-Polymer.

4. A process as defined in claim 3 wherein the additive is a plurality of
SEBS polystyrene elastomer particles.

5. A process as defined in claim 4 wherein sufficient particles of SEBS
are added to form 20-30% of the mixture.

6. A process as defined in claim 4 wherein the range in average particle
size is between 200 nm to 1500 nm.

7. A process as defined in claim 4 wherein the mixture provides a flow
rate of between 4 grams per 10 minutes and 12 grams per 10 minutes in
standardized ASTM testing.

8. A process of forming a structure using an additive process modeling
machine comprising:building up a modeling medium based upon design data
provided from a computer aided design (CAD) system, wherein the modeling
medium is an amorphous vinyl alcohol polymer material.

9. A process as defined in claim 8 wherein the model is a support
structure for another model.

10. A process as defined in claim 8 wherein the amorphous vinyl alcohol
polymer is G-Polymer®

11. In a process for making a three-dimensional object by dispensing
solidifiable modeling material in a predetermined pattern so as to define
the three-dimensional object in coordination with dispensing solidifiable
support material so as to define a support structure for the
three-dimensional object, the support structure thereby having portions
thereof in contact with the object, the improvement comprising: forming
at least those portions of the support structure contacting the object or
the object from an amorphous vinyl alcohol polymer.

[0002]This invention relates generally to the fabrication of
three-dimensional objects using additive process modeling techniques.
More particularly, the invention relates to forming three-dimensional
objects by depositing solidifiable material in a predetermined pattern
and providing support structures to support portions of such a
three-dimensional object as it is being built.

BACKGROUND OF THE INVENTION

[0003]U.S. Pat. Nos. 6,228,923 and 6,790,403 incorporated herein by
reference, assigned to Stratasys Inc of Eden Prairie, Minn., disclose
soluble materials used as support structures in fused deposition
modelling (FDM®) methods. A layer by layer method of depositing
materials for building a model is described in U.S. Pat. No. 5,121,329
incorporated herein by reference, and numerous other patents assigned to
Stratasys, Inc. relate to a fused deposition method or FDM® methods of
model deposition.

[0004]Additive process modeling machines form three-dimensional models by
building up a modeling medium based upon design data provided from a
computer aided design (CAD) system. Three-dimensional models are used for
functions including aesthetic judgments, proofing the mathematical CAD
model, forming hard tooling, studying interference and space allocation,
and testing functionality. A common technique is to deposit solidifiable
modeling material in a predetermined pattern, according to design data
provided from a CAD system, with the build-up of multiple layers forming
the model.

[0005]In creating three dimensional objects by additive process
techniques, such as by depositing layers of solidifiable material,
supporting layers or structures must be used underneath overhanging
portions or in cavities of objects under construction, which are not
directly supported by the modeling material itself.

[0006]A support structure may be built utilizing the same deposition
techniques and apparatus by which the modeling material is deposited. The
apparatus, under appropriate software control, produces additional
geometry acting as a support structure for the overhanging or free-space
segments of the object being formed. Support material is deposited either
from a separate dispensing head within the modeling apparatus, or by the
same dispensing head that deposits modeling material. The support
material is chosen so that it adheres to the modeling material. Anchoring
the model to such support structures solves the problem of building the
model, but creates the additional problem of removing the support
structure from the finished model without causing damage to the model.

[0007]U.S. Pat. No. 6,228,923 in the name of Lombardi et al., assigned to
Stratasys, Inc. discloses the use of poly(2ethyl-2-oxazoline) or PEO, a
variety of which is commercially available under the name Aquazol®.
PEO is a polar water soluble polymer with rheology and mechanical
material properties suitable for use in FDM machines as feedstock.

[0008]U.S. Pat. No. 6,790,403 in the name of Priedeman, Jr. et al.,
assigned to Stratasys, Inc., refers to the use of a polymer consisting of
a carboxylic acid base and plasticizer, that is soluble in an alkali
solution.

[0009]One drawback with Carboxylic acid based polymer is that there is not
a great range of temperatures in which it can be used before it degrades
and cannot be used. The Carboxylic acid polymer operates at less than 240
degrees C. (<470 degrees F.) in FDM®. We have found that if the
Carboxylic melt temperature remains above that for an extended period the
material will start to degrade and fail in the machine. Another drawback
which we perceive with using Carboxylic acid based polymers is that they
are alkali soluble. The alkaline solution required to dissolve the
Carboxylic based polymer is noxious, corrosive to skin, an irritant to
eyes, and is generally incompatible to an office environment wherein the
FDM® are intended to operate.

[0010]A further drawback of the carboxylic acid based polymer is that its
glass transition point (Tg) is lower than the envelope temperatures
required for deposition of polycarbonate (PC) and polyphenylsulfone
(PPSF) materials currently used in FDM machines. If used in this
application, the carboxylic acid based polymer would soften and would be
unable to act as a support structure.

[0011]It is an object of this invention to provide a polymer that is water
soluble facilitating dissolving the support and making the process less
hazardous. FDM machines using the soluble support media described above
have software controls controlling support temp so that it cycles around
230 degree C.

[0012]It is an object of this invention to use a water soluble polymer
having greater operating temperature headroom to work at that
temperature.

SUMMARY OF THE INVENTION

[0013]In accordance with this invention a water-soluble amorphous vinyl
alcohol polymer is used as a deposition modeling support material. A
preferred form of the material is commercially available as Nichigo
G-Polymer® from Nippon Gohsei of Japan.

[0014]In accordance with an embodiment of the invention, in a process for
making a three-dimensional object by dispensing solidifiable modeling
material in a predetermined pattern so as to define the three-dimensional
object in coordination with dispensing solidifiable support material so
as to define a support structure for the three-dimensional object, the
support structure thereby having portions thereof in contact with the
object, an improvement comprising: forming at least those portions of the
support structure contacting the object, or the object itself from an
amorphous vinyl alcohol polymer.

[0015]In accordance with an aspect of the invention, a mixtre of Nichigo
G-Polymer® and plasticizer such as SEBS is used in a 3-D dispensing
modeling machine for forming a support structure or as the model itself.

[0016]In accordance with another broad aspect of the invention, SEBS
plasticizer is mixed with a polymer in a 3-D dispensing modeling machine.
Preferably this is mixed with G-Polymer, however could be used with other
polymers suitable for use in 3-D dispensing modeling machines.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]Exemplary embodiments of the invention will now be described in
conduction with the drawings, in which:

[0018]FIG. 1 is a diagrammatic illustration of a model formed by a
filament-feed extrusion apparatus wherein the Nichigo G-Polymer®
material of the present invention is used as material B to form a support
structure.

[0019]FIG. 2 is a perspective view (portions broken away) of the model of
FIG. 1 in a water bath used in practicing the process of the present
invention.

DETAILED DESCRIPTION

[0020]Referring now to FIG. 1 an extrusion apparatus 10 is shown for
building a model 26 supported by a support structure 28 according to the
present invention. The extrusion apparatus 10 includes an extrusion head
12, a material-receiving base 14, a filament supply spool 16 and a
control 18. Extrusion head 12 moves in X and Y directions with respect to
base 14, which moves in a vertical or Z direction. Supply spool 16
supplies a flexible filament 20 to extrusion head 12. Filament 20
typically follows a rather tortuous path through extrusion apparatus 10,
and is advanced towards extrusion head 12 by means of stepper
motor-driven pinch rollers. Filament 20 is melted in a liquifier 22,
carried by extrusion head 12. The liquifier 22 heats the filament to a
temperature slightly above its solidification point, reducing it to a
molten state. Molten material is extruded through an orifice 24 of
liquifier 22 onto base 14.

[0021]The extrusion apparatus 10 of the disclosed embodiment has no
positive cut-off valve for stopping flow of the molten material through
orifice 24 when a layer or a pass is complete. The flow is stopped by
ceasing to advance filament 20 into extrusion head 12. The flow rate at
which the molten material is dispensed onto base 14 is determined by a
combination of the orifice size and the rate at which filament 20 is
advanced into extrusion head 12.

[0022]The movement of extrusion head 12 is controlled by control 18 so as
to deposit material onto base 14 in multiple passes and layers to build
three-dimensional model 26 having a shape determined by stored CAD data
and further to build support structure 28 defined so as to physically
support the model 26 as it is being built. The model 26 and Its support
structure 28 are built up on the base 14 within a build envelope having
an environment controlled to promote solidification. A first layer of the
deposited material adheres to the base so as to form a foundation, while
subsequent layers of material adhere to one other. A base that has been
successfully used is a polymer foam removably mounted to a platform.
Other materials that may serve as a base include sandpaper formed of a
fine wire mesh screen coated with sand and adhered to a platform, a
water-soluble wax, a foam plastic material, and an acrylic sheet mounted
to a vacuum platen.

[0023]A modeling material A is dispensed to form the model 26.
G-Polymer® support material B is dispensed in coordination with the
dispensing of modeling material A to form the support structure 28.
Common materials used for A are ABS, PC, PC-ABS blends, nylons and less
commonly used is PPSF. For convenience, the extrusion apparatus 10 is
shown with only one filament supply spool 16 providing a single filament
20. It should be understood, however, that in the practice of the present
invention using a filament-feed apparatus such as disclosed herein the
modeling material A and the water soluable G-Polymer® support material
B are provided to the extrusion apparatus 10 on separate filament supply
spools. The extrusion apparatus 10 may then accommodate the dispensing of
two different materials by: (1) providing two extrusion heads 12, one
supplied with modeling material A and one supplied with modeling material
B; (2) providing a single extrusion head supplied with both the modeling
material A and the G-Polymer® support material B, with a single nozzle
for dispensing both materials; or (3) providing a single extrusion head
supplied with both materials, with each material dispensed through a
separate nozzle.

[0024]Modeling material A is typically a thermoplastic material that can
be heated relatively rapidly from a solid state to a predetermined
temperature above the solidification temperature of the material, and
preferably has a relatively high tensile strength. An
acrylonitrile-butadiene-styrene (ABS) composition is one particularly
suitable modeling material. Other materials that may be used for the
modeling material A include a variety of waxes, paraffin, a variety of
thermoplastic resins, metals and metal alloys. Glass and chemical setting
materials, including two-part epoxies, would also be suitable.

[0025]Support material B, in the form of G-Polymer® can preferably be
heated relatively rapidly from a solid state filament to a predetermined
temperature above the solidification temperature of the material, and
solidify upon a drop in temperature after being dispensed.

[0026]The soluble support structure 28 created with support material B may
be formed in a known manner, such as disclosed in U.S. Pat. No.
5,503,785, which is hereby incorporated by reference as if set forth
fully herein. FIGS. 3-5 of the '785 patent illustrate a removable support
structure. As shown in FIG. 1 herein, the support structure 28 may be
built entirely out of the support material B. Or, as shown, the
G-Polymer® support material B may form a dissolvable joint between the
model formed of modeling material A and a support structure formed of the
same material A. The joint can be a release layer or layers, or a thin
coating.

[0027]After completion of the model 26, the support structure 28 is
removed from the model 26 by soaking the model 26 with its attached
support structure 28 in a bath 40 containing water. In the embodiment
shown in FIG. 2, bath 40 is an ultrasonic, temperature-controlled bath
which contains a removable mesh basket 42 for holding the model 26. The
temperature of bath 40 is set using a temperature control 44. The water C
is an aqueous solution that can be washed down the drain for disposal.
The temperature of the solution C in bath 40 can be heated to speed
dissolution of support material B. An ultrasonic frequency generator 46
having an on/off switch starts and stops the ultrasonic transmission. The
ultrasonic frequency transmission generates air bubbles which assist in
dissolving away the support material B by vibrating the model.

[0028]Model 26 remains in bath 40 until the support material B dissolves.
The basket 42 is then removed from bath 40. The basket 42 can be placed
in a sink and the solution C rinsed off of the model 26 with water and
washed down the drain. Bath 40 has a drain 48 from which a plug is
removed to drain the solution C from the bath 40.

[0029]As an alternative to removing support structure 28 from the model 26
by dissolving the support material B in a bath, the support material may
be dissolved using water jets operated by hand or by automation.

[0030]The base 14 may be removed from the model 26 before placing the
model in the bath 40. Alternatively, the base 14 may remain adhered to
model 26 as it is placed in bath 40.

[0031]Advantageously, by altering the G-Polymer's degree of crystalline
structure and branching, the polymer's rheological properties such as
melt index, melt point, glass transition and mechanical properties can be
varied and used in higher temperature applications such as those
encountered in applications for PPSF and PC.

[0032]In a preferred embodiment of the invention we altered the G-Polymer
by way of additives; for instance plasticizer was added to the G-Polymer
to reduce the material stiffness to allow it to be wound in filament form
onto standard FDM feedstock reels without breaking. We found that we
could toughen Nichigo G-Polymer® so as to increase its resiliency with
the addition of 20-30% of a styrene-ethylene-butylene-styrene block
copolymer (SEBS) particle. The nano scale SEBS polystyrene elastomer
particle not only allows the material in filament form to bend without
breaking, which helps in winding onto spools and loading into machine,
but it also improves layer to layer bonding of the material between
itself, soluble to soluble; and to the model material, ABS to soluble. An
additional benefit of using the elastomer particle to provide flexibility
and toughness is that it does not affect the G-Polymer® glass
transition temperature (Tg). Typically plasticisers lower the Tg of the
materials to which they are added. Nano scale particles of SEBS were
selected because it was found that larger particles allowed fusion
between the particles during both processing into filament form and
during support deposition in the machine. The resulting fused SEBS
impaired dissolution of the Nichigo G-Polymer® carrier and left a
stringy residue attached to the ABS structures being modeled.

[0033]Initially we used PEO plasticized material as an additive to Nichigo
G-Polymer® however, it was found that the PEO plasticized material did
not provide the layer to layer bonding strength of that demonstrated by
the SEBS. As a result, we preferred the SEBS polystyrene elastomer
particle. Addition of the SEBS particle however, decreased the melt flow
rate of the material in the machine to such a point as to prohibit
building of support structures. A melt flow between 4 grams per 10
minutes and 12 grams per 10 minutes of the blend of GP and SEBS in
standardized American Society for Testing and Materials (ASTM D1238)
testing is preferred for successful depositing the model or the support
materials in the FDM process. In order to improve flow rate, the
molecular weight of the Nichigo G-Polymer® was altered by blending it
proportionately with lighter grades of Nichigo G-Polymer® used for
film and melt spinning applications. Currently the new molecular wt,
16,000 Daltons, of the Nichigo G-Polymer® has sufficient flow such
that we can vary the SEBS load to improve bonding as required and still
have sufficient flow room for other faster or lower temperature
applications. The particle size of the SEBS polystyrene elastomer in the
water soluble Nichigo G-Polymer® ranges from 200 to 1500 nm. The
average particle size is between this range and is approximately within
the range of 600 to 1100 nm and preferably about 900 nm.

[0034]In a preferred embodiment SEBS particles are melt blended to ensure
even distribution in the carrier Nichigo G-Polymer®. The process
involves first creating a master batch of Nichigo G-Polymer® resin
with SEBS particles blended into the a Nichigo G-Polymer® resin using
a twin screw or compounding extruder. The resulting product is then
pelletized and reblended with the virgin Nichigo G-Polymer® resin
pellets of the appropriate grade so that both the desired MW target and
evenly distributed SEBS particle mix are achieved when the pellet mix is
reprocessed through another compounding extrusion process.

[0035]Advantageously, Nichigo G-Polymer® differs from the prior art
Carboxylic acid based polymers having much more room, i.e. >700 F, in
it's operating envelope before it degrades and cannot be used. The
Carboxylic acid polymer operates at less than 240 C (<470 F) in the
Stratasys FDM machines.

[0036]In a preferred embodiment of this invention, Nichigo G-Polymer®
is the amorphous vinyl alcohol polymer of choice for FDM applications and
is suitable for both the deposition model itself and for the support
structure. Nichigo G-Polymer® meets the requirements, which include,
melt flow, melt strength, viscosity, Tg point, shrinkage during cooling,
strength, modulus, toughness, temperature headroom before degradation,
stickiness, ability to withstand high temp residence, solubility,
moisture absorbance from atmosphere, and swell behavior as it absorbs
moisture.

[0037]In summary, forming a model or a support for a model is
significantly less challenging when using Nichigo G-Polymer® which is
water soluable and allows higher operating temperatures than the prior
art Carboxylic melt.

[0038]Furthermore, our blend of, Nichigo G-Polymer® and SEBS allows our
formulation to stick to itself and ABS by virtue of the nano scale
elastomers while making it flexible enough to wind, yet stiff enough to
feed into the machine, all the while without creating a residual "tubes"
of elastomer and hitting the melt flow targets by adjusting the molecular
weight. This is a significant advance in the art.